OpenType glyph ids are 16 bit unsigned integers, but we were using 32
bit integer and abusing the higher bits to set glyph flags. All such
abuses are now gone and we can make it a simple 16 bit integer.

Change-Id: I594068675f239fd525376fd9ea752462ec3edd9d
Reviewed-on: https://gerrit.libreoffice.org/53270Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Khaled Hosny <khaledhosny@eglug.org>